If they are to be given a colored finish, cement- and lime-bonded building materials, such as plasters, lime-sand bricks, fiber cement parts or cast stones, more particularly roof tiles and paving setts and also flagstones, are generally colored with inorganic pigments. Thus, it is standard practice in the building materials industry to use iron oxides or iron oxide hydroxides as red, black, brown or yellow pigments; manganese oxides as brown-black pigments; chromium oxides as green pigments and titanium dioxides as white pigments. Further examples of inorganic pigments are carbon blacks as black pigments, nickel or chromium rutiles as yellow pigments and cobalt-containing spinels as blue and green pigments, copper-containing spinels as black pigments and mixed crystals of barium sulfate and barium manganate as blue pigments.
For coloring concrete products, the pigments are normally used in powder form. In ground form, they have the advantage of ready dispersibility. Pigment powders are dispersed completely homogeneously in concrete mixtures in a short time of up to a few minutes. The disadvantage of fine powders is that they show poor flow behavior and often agglomerate and cake in storage. Exact metering is thus made difficult. Another disadvantage of certain powders is that they tend to emit dust.
It is known that these disadvantages in the pigmenting of concrete parts can be avoided by using aqueous pigment suspensions instead of dry pigment powders. These aqueous suspensions (pastes or slurries), which contain 30 to 70% by weight pigment, have never been widely used because the additional water content can give rise to considerably higher transport costs, depending on the distance from the factory to the user. In addition, the large quantity of water supplied with the slurry cannot be processed in every concrete preparation.
Accordingly, the building materials industry has largely continued to use dry pigment powders. Hitherto, the use of pigments in the form of microgranules, of the type known from the plastic and paint industries, has suffered because it was thought that granules would be less readily dispersible in concrete preparations. Poorly dispersible pigment agglomerates would require much longer mixing times. With the normally short mixing times widely used in the building materials industry, fish eyes, streaks or pigment agglomerates would occur at the surface of the concrete as a result of poor pigment distribution. The strength of color present in the pigment would not be developed, so that larger quantities of pigment would have to be used for the same color intensity of the concrete workpiece.
DE-C 36 19 363 describes pigment granules for coloring concrete products which consist essentially of pigment and one or more binder(s) promoting the dispersion of the pigment in the concrete. Binders which function as dispersion aids in concrete are said to include alkylbenzene sulfonate, alkyl naphthalene sulfonate, lignin sulfonate, sulfated polyglycol ethers, melamine/formaldehyde condensates, naphthalene/formaldehyde condensates, gluconic acid, salts of low molecular weight partly esterified styrene/maleic anhydride copolymers and copolymers of vinyl acetate and crotonic acid. The percentage content in the pigment is said preferably to be 2 to 6% by weight.
The dispersion aids mentioned act as liquefiers in concrete mixtures. They influence the water-to-cement ratio and, hence, the consistency of the concrete.
In the inorganic pigment itself, the binders added-- as organic substances--represent foreign bodies.
According to DE-A 29 40 156, the inorganic starting pigment has a resin content of at least 20%. The dispersion of corresponding granules in concrete is seriously complicated by the resin components of hydrophobic agglomerates.